October 28, 2015

October 22, 2015

This paper used the same data as the Allentoft et al. paper, but instead of focusing on the human DNA recovered from ancient Eurasians, it went looking for interesting stuff in the non-human DNA (the stuff that is usually thrown away).

The result: 2,800-5,000 year old Yersinia pestis from Europe to the Altai. It will be cool to look at even older remains than the Bronze Age, but this already pushes the date for plague by a couple thousand years, and implicates steppe people in its earliest spread.

The bacteria Yersinia pestis is the etiological agent of plague and has caused human pandemics with millions of deaths in historic times. How and when it originated remains contentious. Here, we report the oldest direct evidence of Yersinia pestis identified by ancient DNA in human teeth from Asia and Europe dating from 2,800 to 5,000 years ago. By sequencing the genomes, we find that these ancient plague strains are basal to all known Yersinia pestis. We find the origins of the Yersinia pestis lineage to be at least two times older than previous estimates. We also identify a temporal sequence of genetic changes that lead to increased virulence and the emergence of the bubonic plague. Our results show that plague infection was endemic in the human populations of Eurasia at least 3,000 years before any historical recordings of pandemics.

October 15, 2015

Another (?)-worthy paper has just appeared in Nature in the heels of the African ancient genome paper. Time will tell how these worldview-altering discoveries will change the story of Mankind, and a degree of skepticism is warranted. In the view I've held for a few years, modern humans expanded to Arabia before 100 thousand years ago, started leaving it 70 thousand years ago as the ecological situation worsened due to desertification and broke through the "Neandertal barrier" between 70-50 thousand years ago when they developed the skills and technology to overcome them.

The new paper claims that modern humans were in China 80 thousand years ago and came to Europe much later because Neandertal represented a barrier to successful entry to Europe. This begs the question of how they reached China without encountering Neandertals, as Neandertals were also in West Asia where -presumably- they passed through to get to China. A coastal route to south China would explain away this problem, but the coastal migration is usually envisioned much later, at around 60 thousand years ago. On top of that, how did Chinese end up having equal (or more) levels of Neandertals admixture if modern humans first went to China and later moved west and successfully outcompeted the Neandertals. How were they able to do so eventually? (There is no evidence that the kind of advantages associated with behavioral modernity first emerged in East Asia). It's possible that there were 80 thousand year-old modern humans in China (just as there were 100 thousand year-old modern humans in Israel), but that the later East Asians are not descended from them.

One would think that science would present an increasingly reasonable and consistent picture of the past, but it seems that we're a very long way from the point where the dust settles and the puzzle pieces start falling into place.

The hominin record from southern Asia for the early Late Pleistocene epoch is scarce. Well-dated and well-preserved fossils older than ~45,000 years that can be unequivocally attributed to Homo sapiens are lacking1, 2, 3, 4. Here we present evidence from the newly excavated Fuyan Cave in Daoxian (southern China). This site has provided 47 human teeth dated to more than 80,000 years old, and with an inferred maximum age of 120,000 years. The morphological and metric assessment of this sample supports its unequivocal assignment to H. sapiens. The Daoxian sample is more derived than any other anatomically modern humans, resembling middle-to-late Late Pleistocene specimens and even contemporary humans. Our study shows that fully modern morphologies were present in southern China 30,000–70,000 years earlier than in the Levant and Europe5, 6, 7. Our data fill a chronological and geographical gap that is relevant for understanding when H. sapiens first appeared in southern Asia. The Daoxian teeth also support the hypothesis that during the same period, southern China was inhabited by more derived populations than central and northern China. This evidence is important for the study of dispersal routes of modern humans. Finally, our results are relevant to exploring the reasons for the relatively late entry of H. sapiens into Europe. Some studies have investigated how the competition with H. sapiens may have caused Neanderthals’ extinction (see ref. 8 and references therein). Notably, although fully modern humans were already present in southern China at least as early as ~80,000 years ago, there is no evidence that they entered Europe before ~45,000 years ago. This could indicate that H. neanderthalensis was indeed an additional ecological barrier for modern humans, who could only enter Europe when the demise of Neanderthals had already started.

October 08, 2015

It is no longer tenable to view West Eurasian back-migrations as limited events that affected only North and East Africa: their effects are clearly evident throughout Africa, having affected different populations to a different extent.

A new paper in Science seems to confirm West Eurasian admixture related to Early Neolithic farmers throughout Africa, including the Yoruba, and Mbuti. I haven't read the paper yet, but it would be a striking discovery if confirmed.

UPDATE (1/26/2016). An erratum has now appeared that rejects the claim for Eurasian admixture in all Africans which was the result of the bioinformatic error. I continue to think that there was Eurasian back-migration into Africa, but it was a long shot that this had happened in the last 4,500 years (hence the ? in the title of this entry). A time series of African DNA may show whether the null model of Sub-Saharan Africans receiving virtually no admixture from Eurasia for the entirety of the existence of H. sapiens can remain valid.

Characterizing genetic diversity in Africa is a crucial step for most analyses reconstructing the evolutionary history of anatomically modern humans. However, historic migrations from Eurasia into Africa have affected many contemporary populations, confounding inferences. Here, we present a 12.5x coverage ancient genome of an Ethiopian male (‘Mota’) who lived approximately 4,500 years ago. We use this genome to demonstrate that the Eurasian backflow into Africa came from a population closely related to Early Neolithic farmers, who had colonized Europe 4,000 years earlier. The extent of this backflow was much greater than previously reported, reaching all the way to Central, West and Southern Africa, affecting even populations such as Yoruba and Mbuti, previously thought to be relatively unadmixed, who harbor 6-7% Eurasian ancestry.

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